Predator control around wetlands

A wetland is an area that is saturated by water for most (or all) of the time. To form a wetland, surface water either collects at ground level or it seeps up from below the ground.


Why are wetlands so important?

Rivers, lakes, streams, ponds, swamps, bogs, and estuaries all provide important and diverse habitats and seasonal food resources for a range of valued and diverse wildlife, such as waterfowl and other birdlife, fish, tuna (eels) and bees, and including rare and endemic species such as fernbirds, New Zealand dabchicks and scaup, shoveler, and paradise shelducks. 

Wetlands act as a giant sponge – during heavy rain they quickly absorb water into the soil, slowing potential floods. In the drier summer months they release the water to maintain water flow. Wetlands also improve water quality by filtering nutrients and sediments.

Wetlands have historical and spiritual significance for Māori. Wetland plants such as harakeke have long been used for clothing, mats, medicine and dyes. Wetland animals, especially tuna (eels), are valuable food sources.

There is a growing appreciation for wetlands as precious habitats, with diverse wildlife. They play a vital role for people, animals, and for our environment. However, many of our wetlands have disappeared or been reduced, and their wildlife has come under serious threat.

Dabchick
Dabchick. Image credit: Oscar Thomas (iNaturalist NZ)

What threats are faced by wetland animals?

Some animals can only live in wetlands and are facing habitat loss or damage from pollution and wetland drainage. Some are already endangered, such as the bittern, the short-jawed kokopu, and the mudfish.

Unfortunately, wetlands are also havens for introduced predators including rodents, possums and mustelids, who all favour the protection provided by these areas, and their impact on wildlife can be devastating:

  • possums, hedgehogs, stoats, weasels, ferrets, feral cats and rodents all eat birds’ eggs and most will also eat chicks and adult birds 
  • magpies are territorial and aggressive to other birds 
  • rabbits, hares and possums eat wetland plants 
  • dogs may harass wetland birds. 

Wetland and riparian margin predator control needs to target all types of predator. Here, we have focused on possums, rodents, and mustelids (ferrets, stoats and weasels).


Possum control

Willow buds
Willow buds. Image credit: Dzhus Maxim (iNaturalist)

Option 1: Shooting and traps

  • Night-shoot wetland willows as bud-break occurs in spring. Shoot on 3 or 4 nights over a 2–3 week period. Warm nights are best, especially after rain. 
  • Follow up with kill traps (Timms or Sentinel) at 100–150m spacings along wetland margins. 
  • Service and re-bait traps every 2–4 weeks, depending on the population.

Option 2: Bait stations

  • If pigs are not present, use bait stations 30cm off the ground at 150m spacings on trees, well away from stock access along the inside of fence-lines. 
  • Use Pestoff Brodifacoum possum baits in Philproof ‘mini’ bait stations. 
  • Pulse 700g of bait initially and then 300g of bait per station every 4 weeks from late winter (August) to early spring (until late October). 
  • Where there are ‘non target’ species at risk, use 2–3 applications of Feracol or DECAL over the same period, pre-feed with the equivalent non-toxic product for one week before each toxin application. 
  • Both of these products will also control rats. 
  • ’Double Tap’ pellets are a combination of Cholecalciferol and Diphacinone that can also control rats and possums with reduced non target risks. 
  • Ensure dogs and any livestock CAN NOT access any bait.

Rodent control

Traps:

  • Goodnature A24 automatic resetting traps are ideal. Locate at 75–100m intervals about 10–20cm off the ground on trees away from any stock access along the inside of fence-lines.
  • Replace CO2 gas canisters and lure pumps about every 3–4 months. 
  • Rodent snap-traps can also be used (they are cheaper). Place in small wooden tunnels set up in a similar way to A24 networks. Lure with peanut butter. Check regularly every 1–4 weeks.

Bait stations:

  • During times of higher rodent populations, bait stations may be more effective. The same network of bait stations as for possums can be used, but extra traps or stations may be required in between to reduce spacing to 50–75m. 
  • Pulse with Pindone pellets, Ditrac, Contrac or Pestoff (blocks or pellets) monthly, from August to November. 
  • ’Double Tap’ pellets are a combination of Cholecalciferol and Diphacinone that can also control rats and possums with reduced non target risks 
  • Ensure dogs and livestock CAN NOT access any bait.

Stoat, ferret and weasel control

  • Use DOC 200 wooden box traps with enlarged openings (4×4 mesh squares) to target weasels, stoats and ferrets. 
  • Place away from stock access at 100–150m intervals along the inside wetland and/or stream margin fence lines. 
  • Rebait about every 2 weeks with eggs, fresh rabbit (in winter), or Erayz rabbit blocks/paste (a long-life product) in warmer climates. Rebait less in winter and more in spring/summer. 
  • DOC 200 traps also catch rats and hedgehogs. 
  • Modifications may be required if kiwi, weka or other non-target species are present.

Tips for all traps and bait stations

  • Lure the area around and above each trap or bait station site with scented (peach, vanilla, cinnamon) flour laced with icing sugar, again to increase interest. DO NOT put flour on your devices! 
  • A combination of bait types and trapping over time is best practice to avoid predators adapting to your control methods.
  • Make sure grass is controlled at trap or bait station entrances, at least one metre from the entrances. This reduces moisture which causes the bait to go mouldy and makes access easier for predators. Use glyphosate at the start of each season to save time. 
  • Scuff the ground around traps at each check. This creates ‘interest’ for predators.

How else can wetlands be protected?